Since the mid-1980's, studies on a biological processing technique among various methods for processing volatile organic compounds (VOCs) and odor which are released into the atmosphere has been earnestly performed in Europe and since the 1990's, a technique which removes the VOCs or odor from the contaminated air has become as a major issue in view of air pollution. According to the biological processing technique (Biofiltration), a reactor is filled with a filler including a microbial membrane and contaminated air passes through the filler to diffuse the contaminated material into the microbial membrane and oxidation-decompose the contaminated material by the microorganism, thereby purifying the contaminated air.
The biological removal technique has been known as a technique which is more economical and broadly applicable than a physicochemical processing technique of the related art such as an incineration method and an active carbon adsorption process which process the VOCs in terms of low cost equipment and low operating cost and is very useful in purifying contaminated air which is generated at a low concentration with a large amount.
Historically, as a biofilter in an early stage which has been used from the 1960's, a soil bed in which contaminated air is injected into a soil layer to be removed by soil adsorption and soil microorganism has been used. Even though an effect of removing 90% or more of VOCs and odor by the method is admitted, a large space is required for the soil bed and there is a technical problem of supplying uniform air into the soil layer in addition to high pressure loss.
Since the 1980's, as a filler of the biofilter, organic materials such as compost, peat, or a wood bark have been mainly used to process the odor and the VOCs. However, even though the organic filler has high removal efficiency due to high physical adsorption and good water retention capacity, the filler is decomposed by the microorganism and consolidated due to mineralization, so that air flow to the filler layer is not uniformly maintained.
Due to such a problem, the organic filler needs to be replaced or rearranged every year to maintain processing efficiency. Recently, in order to compensate for the problem of the organic filler, there is an attempt to mix the organic material such as compost, peat, or wood bark and an inorganic material such as plastic, pellet active carbon, or ceramic to improve the efficiency of the biofilter.
When the VOCs are processed by the biofilter of the related art which uses an organic matter as a filler, the microorganisms decompose the VOCs to use it as a carbon source so that the microorganisms are grown. Therefore, when the filler is attached thereto so that the microorganisms are overgrown, the overgrown microorganism (biomass) blocks an air gap of the filler which causes a pressure loss, so that processed air volume is reduced and processing efficiency is lowered, and thus entire removal efficiency is lowered. Also in a trickling air biofilter, an excessive pressure loss due to proliferation of overgrown surplus microorganism is caused. In order to solve the above-mentioned problem, an American inventor, Soriel et. al. (1997), invented a method of suppressing a microorganism from being grown using NaCl, but the method results in hindrance of growth and development of the microorganism and rapid reduction of the processing efficiency. Further, in a sulfur based component such as hydrogen sulfide, methyl sulfide, dimethyl disulfide, or methyl mercaptan or a nitrogen based component such as ammonia which is an inorganic odor material, blockage due to proliferation of excessive microorganisms does not matter. However, one of the most effective methods for increasing efficiency is to maintain a uniform microorganism concentration between an upper part and a lower part of a reactor.
It is very inefficient to provide a contaminated air purifying device which consumes high energy around an industrial complex where contaminated air is always discharged or in an area where other order is continuously distributed and generated and specifically, cost for frequently replacing a consumable filter is high.
Therefore, it is required to reduce soluble contaminated air which is discharged from the industrial complex or the area where other odor is continuously generated using an eco-friendly effective microorganism at low cost in a daily life and implement an eco-friendly self-independent device.